1. Field of the Invention
The present invention relates, for example, to a bush for a vehicle to be mounted on a suspension arm or the like included in a vehicle such as an automobile.
2. Description of the Related Art
For example, Japanese Patent Application Publication No. 2010-159844 (hereinafter referred to as Patent Document 1) discloses a configuration of a bush to be mounted on a suspension arm or the like of an automobile. The bush of Patent Document 1 includes: an outer cylinder; an inner cylinder; an elastic body made of rubber or the like, and interposed between the outer cylinder and the inner cylinder; and an intermediate member embedded in the elastic body, and made from a resin material more rigid than the elastic body. The intermediate member is formed in a cylindrical shape to surround the inner cylinder, and includes a slit extending in an axial direction of the intermediate member. In the case of the bush of Patent Document 1, the drawing of the outer cylinder narrows the widths of the slits, reduces the diameter of the intermediate member, and thereby compresses the inner portion of the elastic body which is located inside the intermediate member. The bush of Patent Document 1 can make the rigidity of the elastic body higher (increase its spring constant), since the drawing of the outer cylinder can make the number of parts smaller than before, and concurrently can compress the inner and outer portions of the elastic body which are located respectively inside and outside the intermediate member.
In the rubber used in the bush of Patent Document 1, there is a trade-off between the spring constant and the performance of damping vibrations which occur, for example, when a tire travels over a bump on a road surface (hereinafter referred to as a “vibration damping performance”). In other words, the vibration damping performance of the rubber becomes higher as the spring constant becomes smaller, and becomes lower as the spring constant becomes higher.
Furthermore, in the rubber, the spring constant becomes higher as the vibration frequency becomes higher. In other words, in the rubber, the vibration damping performance becomes lower as the vibration frequency becomes higher. If as mentioned above, the vibration damping performance of the rubber becomes lower, the performance of suppressing noises and vibrations (hereinafter referred to as an “NV performance) becomes lower, and the ride comfort is worsened.